ABS False Activation - please help

[rossocorsa]

I think the reason for a false low speed ABS activation is very very small differences in the signal between the two sensors this makes the abs ECU 'think' that there is a lock up situation and activates, I had this after a sensor change i think it's due to fractionally incorrect seating of a sensor or dirt on the bearing,also I've seen the theory on the 'net somewhere that slight surface corrosion under the sensor can be enough to very slightly lift it causing marginally differing signals

[Anthony & Maricel]

Mine was due to the wear of the sensor cable on the inside hub which eventually wore through the cable, this caused the same symptoms ABS activating at slow speed and eventually the abs light came on.

Something to look for when ABS problems start to occur.

[James.uk]

The two front abs sensors I bought were £75 each!

And yes a tiny bit of foreign matter under the ABS sensor can cause the ABS to come on at times..

I am having the same problem, but it is getting better all the time..
...

[Anthony & Maricel]

They are £17 ea on ebay, so check ebay before allowing a greasy monkey to charge you lots of wonga + labour

[BigRuss]

Originally Posted by rossocorsa

I think the reason for a false low speed ABS activation is very very small differences in the signal between the two sensors this makes the abs ECU 'think' that there is a lock up situation and activates, I had this after a sensor change i think it's due to fractionally incorrect seating of a sensor or dirt on the bearing,also I've seen the theory on the 'net somewhere that slight surface corrosion under the sensor can be enough to very slightly lift it causing marginally differing signals

A distinct possibility, these are what are known as plausibility faults on the abs system when you diagnose it on T4.

the cause is as you say dirt, corrosion, damaged bearing surface or a badly seated sensor.

The variance in signal isn't enough to illuminate the warning lamp but may be enough to cause the problem as described.

Sometimes it will clear on it's own if it's down to dirt, but corrosion or a badly seated sensor would require the removal and replacement of the sensor to fix it.

Just a point here, there seems reading this thread to be an assumption that it's down to one of the front sensors causing the problem, it may well be one of the rear ones

Russ